NOx emission requirements and particulate standards are becoming more stringent in many markets. Internal combustion engines may be equipped with a NOx sensor in the exhaust system to determine whether the NOx levels are acceptable according to the applicable requirements, and also to optimize engine performance and control one or more outputs of the system in response to measurements from the NOx sensor.
The outputs of a NOx sensor may be monitored by an on-board diagnostic (OBD) system of the associated engine system and compared to an expected output based on one or more other known conditions to detect a fault condition associated with the NOx sensor. If the OBD indication that a NOx sensor is faulty is incorrect, unnecessary derate conditions or service events can result, increasing operating and service costs in addition to operator and owner inconvenience. Furthermore, if outputs of the system are controlled based on NOx sensor measurements during periods of operation in which the NOx sensor measurements are unreliable, engine and/or exhaust aftertreatment system performance may be compromised.
Therefore, a need remains for further improvements in systems, apparatus, and methods that determine operating conditions that result in unreliable NOx sensor outputs and/or measurements to avoid determining one or more system outputs in response to the NOx sensor measurements during such conditions.